WBR0973
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| Author | [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Yazan Daaboul, M.D.)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::Variations in blood and urine concentrations of a molecule X are analyzed in two groups of rats fed with either high protein or low protein diet. Shown below is the structure of molecule X. In this molecule, carbon dioxide is the donor of the carbon and oxygen moieties, while ammonia is the donor of one amino group moiety. Which of the following amino acids is the donor of the second amino group moiety in molecule X?
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| Answer A | AnswerA::Aspartate |
| Answer A Explanation | [[AnswerAExp::Aspartate is the donor of the second amino group of the urea molecule.]] |
| Answer B | AnswerB::Arginine |
| Answer B Explanation | [[AnswerBExp::Arginine is not the donor of the second amino group of the urea molecule.]] |
| Answer C | AnswerC::Lysine |
| Answer C Explanation | [[AnswerCExp::Lysine is not the donor of the second amino group of the urea molecule.]] |
| Answer D | AnswerD::Fumarate |
| Answer D Explanation | [[AnswerDExp::Fumarate is not the donor of the second amino group of the urea molecule.]] |
| Answer E | AnswerE::Alanine |
| Answer E Explanation | [[AnswerEExp::Alanine is not the donor of the second amino group of the urea molecule.]] |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::One molecule of urea (molecule X of this vignette) is composed of two amino groups (-NH2), one carbon atom (C), and one oxygen atom (O). Both the carbon and oxygen atoms are donated from carbon dioxide. One amino group is donated from ammonia, while the other amino group is donated from the amino acid aspartate. Educational Objective: The urea molecule is composed of 2 amino groups, 1 carbon atom, and 1 oxygen atom. One amino group is donated from ammonia, while the other amino group is donated from the amino acid aspartate. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Urea, WBRKeyword::Amino group, WBRKeyword::Aspartate, WBRKeyword::Carbon dioxide, WBRKeyword::Amino acid, WBRKeyword::Molecule X |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
